One of the goals of current research on cell signaling and receptor activation is to enable therapeutic modulation of processes involved in cell growth and survival. Such processes determine outcome in diverse medical conditions, including organ failure, fetal development, and tumor growth, among others. Each of these conditions is of worldwide clinical importance, and has limited efficacious treatment options. It is an object of the invention to provide compositions and methods for promoting regeneration or survival of damaged tissue, as well as for treating disorders involving the aberrant growth and development of tissues.
Tissue loss or end-stage organ failure affects millions of people worldwide each year and adds substantially to health care costs. Organ or tissue loss is usually treated by transplanting organs from donors, by surgical reconstruction, or with mechanical devices. Each of these remedies has shortcomings. Transplantation is limited by donor shortage, surgical reconstruction can create other long-term problems, and mechanical devices cannot perform all the functions of a single organ, and therefore cannot prevent progressive deterioration. Thus, a real medical need exists for new solutions to these problems.
Protein factors that affect the growth, differentiation and/or survival of cells may be useful in the treatment of disorders of organs which contain responsive cells. Factors or ligands that interact with receptors of the receptor protein tyrosine kinase (RPTK) family are of particular interest in this regard. These receptors are involved in many cellular programs including cell growth and differentiation, and the genesis of many neoplasias. Thus the factors or ligands that interact with these receptors may prove useful in treating disorders of certain organs where the tissue has been damaged. Alternatively, it may be useful to block the interaction of these factors with their receptors in order to block tumor growth.
The Ret proto-oncogene encodes a receptor tyrosine kinase that is expressed during development in a variety of tissues, including the peripheral and central nervous systems and the kidney. The abnormalities present in ret null mice suggest that Ret is critical for the migration and innervation of enteric neurons to the hindgut, and for proliferation and branching of the ureteric bud epithelium during kidney development (Nature 367, 380-383, 1994). The search for a key component of the Ret signaling pathway, the Ret ligand, has been an area of intensive research.